When the 2nd amendment was adopted, the armed citizenry was much closer to being equal to the government in firepower. True, the government had cannon, and the citizens did not, but nevertheless citizens were a force to be reckoned with by the government. The capacity for guerrilla warfare was not to be sneezed at, and it was immortalised as the second right in the Bill of Rights.
Today the government has tanks, fighter planes, nukes, and more, while the citizenry has semi-automatic rifles and handguns, which the Democrats would like to take away from them.
This argument that the Founders were talking about muskets and now we are allowing AR-15s, is ridiculous. The point is the disparity between the authorities and the people, which has gotten much larger, not smaller.
If the Founders were around today, they would be legalizing fully automatic weapons and RPGs, at least.